Method of cleaning and pickling metals



Patented Apr. 5, 1932 UNITED STATES Cross Reference PATENT OFFICE WALDO I4. SEMON, OF GUYAHOGA. FALLS, OHIO, ASSIGNOR TO THE B. F. GOODRICE COM- PANY, OF NEW YORK, N. Y A CORPORATION OF NEW YORK METHOD OF GLEANI NG AND PICKLING METALS No Drawing. Application filed April 19,

This invention relates to the art of pickling metals such as iron or steel, that is, to the art of removing scale or rust from the surface of such metals by a process of solution.

It is the common practice to remove scale and rust from the surface of iron or steel by immersion in a dilute solution of sulphuric or hydrochloric (muriat-ic) acid, which is frequently heated to a temperature of about 70 C. to accelerate the solution of the iron oxides. However, the pickling acid, in addition to its dissolving action on the oxides, rapidl attacks the metal'itself, dissolving it 16 and li rating hydrogen gas. A ortion of the hydrogen penetrates the metal and rendejsgmnfivmiwwinder escaping from the liqul an carrying with it some of the acid in the form of a fine mist 20 which is very disagreeable to workmen in the vicinity and rapidly corrodes all metal in the room or building. The attack and solution of the metal is also undesirable because of the consequent loss of metal and of acid,

2 which cannot economically be recovered, and

because of the fact that the process of solution is not uniform, but localized, causing pitting of the surface.

Heretofore the addition of so-called pick- 3" ling inhibitors to the acid has been proposed, such inhibitors possessing the property of re tarding the solution of iron in acid, while not appreciably affecting the solution of its oxides. Among the inhibitors which have been proposed, sugars, proteins, and certain nitrogenous bases have found considerable commercial use.

This invention consists in adding a small 40 proportion of a member of a new class of extremely efl'ective pickling inhibitors to an acid pickling bath. This class of inhibitors hibiting action of the compound. The essen- 1929. Serial No. 356,603.

tial feature is apparently that the heterocyclic nucleus be completely saturated, that is, that the atoms of the rin are joined together, not by double bonds, ut only by single bonds; and that the ring contain at least three different atoms. The rlng will normally contain at least one carbon atom and preferably also at least one nitrogen atom, the third kind of atom being preferably an element of the so-called oxygen group which includes sulphur, oxygen, and selenium, although other elements such as phosphorus, arsenic, etc. may be employed under certain conditions. The nitrogen atom in the ring contributes a basic reaction to the moleculeflnaking it soluble in acid solutions. This property is of considerable importance, since the inhibitory effect of an insoluble material can never be come fully apparent, and since it eliminates the formation of sludge or scum due to the presence of particles or droplets of the inhibitor in the pickling solutions. Other properties desirable in practical pickling inhibitors are stability at temperatures lower than 100 C., stability in the presence of strong acids such as sul huric, hydrochloric, hydrofluoric, or even nitric acid, and low vapor pressure, so that the inhibitor will not be lost by evaporation from the hot pickling solutions customarily employed. These conditions are readily met by numerous substances gelonging to the general class hereinabove dened.

The following compounds, for example, are

typical members of the above-defined class:

(st "Y EmH:

dimethylthetin C{|\ \SOI H anhydrotaurine Examiner rhodanic acid CHI thlaldlne carbothialdlne JILL dlthlo-triphenylguanldine NH0=S NH-O=S t t A xanthane hydride The following tests illustrate clearly the remarkable efliciency of the products of this invention as pickling inhibitors.

Ewample 1.Pickling solutions were prepared containing respectively 5% by weight of hydrochloric (muriatic) acid, 20% hydrochloric acid, 4% and 10% sulphuric acid. Each of these was divided into several portions, one of which was used as a control. To the other portions were added various proportions of the 2-phenylimino 3-phenyl tetrahydrothiazole prepared by reacting diphenylthiourea with eth lene dichloride. Test pieces of sheet steel, a out 2 cm. X 5 cm. in size were cut from a single sheet of metal. The metal strips were all given a preliminary treatment in an acid solution to remove the scale, were washed, bent at right angles, and placed on edge, each in the bottom of a widemouthed bottle. Each bottle was completely filled with one of the acid solutions previously prepared, and closed with a rubber stopper ]pierced by a bent glass tube so ar ranged t at the hydrogengas evolved by the reaction of the acid with the metal displaced an equal volume of the liquid, which flowed through the tube into a measuring device. The bottles were then placed in water baths maintained at constant temperatures, and the volume of hydrogen evolved in a period of one hour was carefully measured.

The results are tabulated below.

Volume of hydrogen evolved, in cubic centimeters ii ii li i l iz ii lis dr iiiiii ii i iio 0733 0%5 07i2 5. 5

4% H 80 at 60 c 14.5 1.9 0.9

10% H280 at 60 c ea 0 a0 2.0 1.0

5%HClat60C 50.0 5.4 2.9

20% He]. at C 153.0 9.2 6.4 3.0

Volume of hydrogen evolved i-n cubic centimeters '51? N 3 1 XBII 8116 1) GUY Pickling inhibitor None hydride morphu line The p-hydroxy N-phenyl morpholine is even more efl'ective than its parent substance, N-phenyl morpholine. For example, the rate of solution of bright mild steel in 20% hydrochloric acid at 40 (3., containing 0.5% of phydroxy N-phenyl morpholine, is only 5 to 7% as great as that of the same metal in the same acid without the inhibitor.

It is evident that the preferred products of this invention are extremely valuable in pre- Venting the corrosion of metals in acid pickling baths. However, the addition of such inhibitors has practically no effect on the rate of solution of the scale or other oxide of the metal.

In the practice of this invention on a commercial scale, an acid solution containing hydrochloric or sulphuric acid is prepared in the usual manner and a small proportion of the inhibitor is dissolved therein, for example one pound of the inhibitor to from one hundred to one thousand pounds of acid being used. The metal, which is preferably first degreased lit;

paratively large proportions, u

by treatment with an organic solvent or with an alkali, is treated in this bath in the customary manner, except that it may be left in the solution for a 1011 er time, since there is little danger of overpic in Pitting of the metal is almost completel eliminated, the consumption of acid and 0 metal is very greatly reduced, and embrittlement of the metal and formation of acid mist due to the evolution of hydrogen gas is largely prevented.

Metals may be pickled or cleaned in many widely difierent manners in the improved pickling solutions containing the inhibitors of the class hereinabove described. For example, the metal may be completely immersed in the acid, if desired, being carried into and out of the solution by automatic devices which also wash and dry the metal; or the solution may be'sprayed onto the surface of the metal, and be later washed ofi by a water. spray. The concentration of the acid and the temperature of the solution may be varied as desired, and the inhibitors may be added in either greater or less proportions than de scribed in the examples above. It is evident that even proportions of less than 0.01% of the inhibitor are quite effective, Whereas comto several per cent, may be necessary to re uce the corrosion of the metal to an absolute minimum. Although either hydrochloric or sulphuric acid is usually employed in pickling iron, because of the low cost of these substances, any of the other non-oxidizing acids may be substituted therefor in whole or in part. For example, pickling solutions containing phosphoric or hydrofluoric acid, or even oxidizing acids such as nitric acid, are useful in many cases.

It will often be found convenient to add the requisite amount of the inhibitor to the concentrated acid at the time of manufacture or at any later time, and simply dilute this stock pickling acid containing the inhibitor to the desired concentration as it is needed. Such a stock pickling acid may, for example, be prepared by dissolving-1 part by weight of one of the hereinabove described inhibitors in 500 parts of concentrated sulphuric acid.

While I have herein disclosed with considerable particularity certain preferred manners of performing my invention, I do not thereby desire or intend to limit myself solely thereto, for, as hitherto stated, the precise proportions of the materials utilized may be varied and other materials having equivalent chemical properties may be em loyed if desired without departing from t e spirit and scope of the invention as defined in the appended claims.

I claim:

1. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound Cross aerate containing at least three difierent atoms in the ring, two of such atoms being carbon and nitrogen, a third being selected from the oxygen group of elements.

2. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound containing carbon, nitrogen and oxygen atoms in the ring.

3. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of a substance selected from the class including morpholine and its substitution products.

4. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of p-hydroxy N-phenyl morpholine.

5. The method which comprises treating iron or steel with a solution comprising sulphuric acid and p-hydroxy N-phenyl morpholine.

6. A pickling solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound containing at least three difierent atoms in the ring, two of such atoms being carbon and nitrogen, a third being selected from the oxygen group of elements.

7-. A pickling solution comprising a strong non-oxidizing acid and a'small proportion of a saturated heterocyclic compound containing carbon, nitrogen and oxygen atoms in the ring.

8. A pickling solution comprising a strong non-oxidizing acid and a small proportion of a substance selected from the class including morpholine and its substitution products.

9. A pickling solution comprising a strong non-oxidizing acid and a small proportion of p-hydroxy N-phenyl morpholine.

10. A pickling solution comprising sulphuric acid and p-hydroxy N-phenyl morpholine.

11. The process of pickling and cleaning metal articles which comprises subjecting said articles to a dilute, non-oxidizing acid having a small amount of Rhodanin dispersed through said acid.

12. A composition of matter for pickling and cleaning metal articles comprising a dilute, non-oxidizing acid and a small amount ofthodanin finely dispersed through said am 13. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound non-oxi zing acid and a small proportion of Q I a a saturated heterocyclic compound containing at least three different atoms in the ring,

two of such atoms being carbon and nitrogen,

the third being sulphur. 15. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of a compound containing a fivemembered, saturated heterocyclic nucleus with carbon, nitrogen and sulphur atoms in the ring.

16. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound containing carbon and nitrogen and a single sul hur atom in the rin 1 The method which comprises treating iron or steel with a solution comprising a portion of a saturated heterocyclic compound containing carbon and sulphur and a single nitrogen atom in the ring.

18. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound containing at least five atoms in the ring, including a single nitrogen atom, and sulphur and carbon atoms. p '19. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of an organic compound containing a five-membered, saturated heterocyclic nucleus with a single nitrogen and a single sulphur atom in the ring.- 20. The method which comprises treating iron or steel with a solution comprising a strong non-oxidizing acid and a small proportion of xanthane hydride.

21. A pickling solution comprising a strong non-oxidizing acid and a small proportion of a compound containing a five-membered, saturated heterocyclic nucleus with carbon, nitrogen and sulphur atoms in the ring.

22. A pickling solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound containing carbon and nitrogen and a single sulphur atom in the rim I 23. A pickling solution comprising a strong non-oxidizing acid and a small procontaining carbon and sulphur and a single nitrogen atom in the ring.

24. A pickling solution comprising a strong non-oxidizing acid and a small proportion of a saturated heterocyclic compound containing at least five atom in the ring, including a single nitrogen atom, and sulphur and carbon atoms.

25. A pickling solution comprising a strong non-oxidizing acid and a small proportion of an organic compound containinga fire-memstrong non-oxidizing acid and a small proportion of a saturated heterocyclic compound bered, saturated heterocyclic nucleus with a single nitrogen and a single sulphur atom in the rin I 26. A pickling solution comprising a strong non-oxidizing acid and a small proportion of xanthane iydride.

In witness whereof I have hereunto set my hand this 13th day of April, 1929.

' WALDO L. SEMON. 

